1. Field of the Invention
The present invention relates to wireless communications. Specifically, the present invention relates to wireless communication schemes that efficiently use both the available spectrum and the bandwidth.
2. Discussion of the Related Art
In designing a system architecture and the communication protocols for a wireless communication system or network, efficient use of the available bandwidth and the spectrum are emphasized. In addition, if the wireless communication network is designed for a wireless messaging application, e.g. two-way paging, the users' mobility further requires that a low power radio frequency (RF) transmission scheme be used, so as to reduce the instantaneous battery power output requirements and to extend overall battery life. However, this low power requirement also results in the user terminal having a relatively short RF transmission range. From a system perspective, for a given geographical area, a shorter RF transmission range in the user terminal requires a larger number of base stations to cover the service needs of that geographical area. The requirements for adequate coverage are especially stringent in a metropolitan area, where the background noise is high.
An addition consideration in designing a mobile wireless network involves the mechanism for locating a user prior to transmitting information to that user by the wireless network. In a prior art two-way paging application, a powerful central transmitter broadcasts the message to all users continuously on one frequency, and the mobile user responds to or acknowledges the information through a local base station on another frequency.
Another method useful in a metropolitan area is point-to-point communication. In the prior art, to provide point-to-point communication, one or more high power transmitters broadcast messages over a large geographical area. These same transmitters are also associated with receivers for receiving return signals from the user. Under this system, however, the mobile user joint requirements of low-power and relative large operating range constrains communication to a very low data rate. This low data rate makes impractical many applications of interest to users of these devices.
In the prior art, a typical cellular system uses a different method that requires all system communication to be conducted between the user and a local base station in the user's vicinity. While this method minimizes the battery power requirement for transmissions from the user, a more sophisticated system architecture is required. In such a system, the wireless network must be able to locate a base station closest to the user (from an RF perspective) before communication can occur. This method is often used for wireless data communications. However, even under this method, the battery life of a mobile user terminal is still compromised because the user terminal has to communicate frequently with a base station to allow the wireless network to track the user's location in order to route any message designating the user. Alternatively, to track the user's location, a polling scheme can be used. Under the polling scheme, each base station periodically polls its service area to identify the mobile units within the service area. However, such a polling scheme is impractical when a large number of base stations are involved.
Thus, in the prior art, two-way wireless communication over a large geographical area requires at least two separate frequencies: one frequency is used for transmitting messages from a central location of the wireless network to a wireless terminal, regardless of whether the terminal is mobile or stationary, and a separate frequency is used for sending messages from the wireless terminal to a base station. In the prior art, such a base station is a radio receiver for receiving messages from the wireless user terminal. Using separate frequencies, the need for a complicated antenna system and complex electronics necessary for separating transmitted and received signals are avoided, thereby reducing total system cost. Different frequencies for transmitting and receiving are also used in a cellular system, which use large groups of adjacent frequencies at the same location.